In order to obtain excellent efficiency from gas turbines, it is necessary to run them at high temperatures, and this requires materials to be developed which have very high creep resistance at these high temperature. The most effective materials in this respect are nickel-based superalloys made by directed solidification and having a structure which is either of the "monocrystalline" type or else of the "column grain" type parts made of "monocrystalline" superalloys in fact comprise a monostalline gamma matrix in which gamma prime particles are dispersed, said particles cohering with the matrix in such a manner that together they possess substantially the same properties as a single crystal.
Column grain superalloys are constituted by juxtaposed elongate grains extending in the solidification direction, with the structure of each grain being similar to that of a "monocrystalline" superalloy.
These prior alloys are made by directed solidification and are used to make turbine blades for aviation purposes. However, they are not suitable for industrial (or ground-based) turbines since their resistance to corrosion over time is inadequate given the very long period of operation of such turbines, generally between 50,000 hours and 100,000 hours. The alloy used most frequently at present for making industrial turbine blades is the alloy called IN 738. It has excellent resistance to corrosion and good resistance to creep. However, with respect to creep, it is much less good than the above-mentioned monostalline or column grain superalloys. Attempts at applying the directed solidification technique to alloys of the IN 738 type have not been successful.
The object of the invention is to provide a nickel-based superalloy which, at high temperatures, simultaneously presents resistance to corrosion that is at least as good as that of the alloy IN 738, together with substantially improved resistance to creep. Such a superalloy is particularly suitable for making the blades of industrial gas turbines, and also for making the second stage blades of aviation gas turbines.